There are many already known processes for the deodorization of malodors, which may mainly be classified into the four species mentioned below.
(i) A physical method by the use of an adsorber for example active carbon (adsorption mechanism). PA1 (ii) A method which relies on chemical reactions such as oxidation and neutralization by the use of chemical substances. PA1 (iii) A biological method by the use of microorganism. PA1 (iv) A masking method by the use of fragrant.
The deodorization mechanism of chlorine dioxide is believed to be an oxidizing reaction which corresponds to the above-mentioned method (ii). Since the presence of chlorine dioxide was published in 1802 by R. Chen-vix, actual preparation of chlorine dioxide was made in 1851 to 1816. Chlorine dioxide is a very explosive and corrosive compound and it was difficult to store and transport the former. When used actually, hence, chlorine dioxide has been produced directly by the user. Chlorine dioxide was, however, focused on its excellent properties such as oxidizing, bleaching and antibacterial activities and so extensive studies were developed in an attempt to seek for a product which is possible to handle easily to everyone. As a result of such studies, there was prepared a compound called stabilized chlorine dioxide into which a stabilizing agent such as alkali or alkaline earth compound is incorporated. The aqueous stabilized chlorine dioxide solution was being adjusted to a pH of 7.5 to 10.0 and made acidic or neutral by the addition of an acidic substance when used thereof. In particular, it is believed that the antibacterial activity of stabilized chlorine dioxide is better at an acidic range than that at an alkaline range. Now, general considerations on the effect and activity of stabilized chlorine dioxide are disclosed in several articles (please refer to J. Odor Research and Eng. vol. 19, pages 328 to 331 (1988); vol. 20, pages 81 to 85 (1989)). The commercially available aqueous stabilized chlorine dioxide solution has a concentration of about 50,000 ppm (approximately 5%) at its maximum, which was employed as such according to this invention.
The stabilized chlorine dioxide has been mainly used in the form of liquid and in other cases there was also known a solid stabilized chlorine dioxide in which the stabilized chlorine dioxide solution was adsorbed on and impregnated into a solid carrier such as zeolite, silica gel, calcium silicate and the like (please refer to Japanese Patent KOKAI No. 63-147468). In case of the aqueous stabilized chlorine dioxide solution, it must be used as such by conventional means e.g. spraying against malodors and so it becomes difficult to use the liquid chlorine dioxide at standard households since it exerts strongly an irritating chlorine smell. In case of the solid stabilized chlorine dioxide adsorbed on and impregnated into zeolite and the like, further, it has been used for the deodorization of refrigerators, but it was difficult to determine a decreased deodorizing activity thereof. As contrary to the liquid stabilized chlorine dioxide, besides, the solid one has a disadvantage of it being of insufficient preservation i.e. stability properties.
In view of the prior art teaching of Japanese Patent Publn. No. 1-38151, for example, it was observed that no storage period of more than one month was possible regarding the stabilized chlorine dioxide in the form of solid which was obtained by adsorbing on and impregnating into a solid carrier such as zeolite and silica gel, following the addition of an acidic substance to the stabilized chlorine dioxide for the activation of the latter. Typical examples of the acidic substance include a solid acid such as alumina and silica-alumina, a mineral acid such as hydrochloric acid and sulfuric acid, and an organic acid such as oxalic acid and citric acid.
We, the present inventors, have made extensive researches in an attempt to dissolve said technical problems, and we have now found that the aqueous stabilized chlorine dioxide solution can be gelled with using both a polyethylene-imine having a molecular weight of from 10,000 to 100,000 and an epoxide crosslinking agent and that there may be obtained a transparent gelled product which has an increased strength, is entirely free of chlorine smell and of long-term stability.